# Maxwell and the speed of light

• I
Einstein said that the speed of light is constant for all observers.

When Maxwell derived that the speed of light in the ether was 299,792,458 m/s could he or did he surmise that the speed of light is constant for all observers (regardless of the motion of the source)?

phinds
Gold Member
Einstein said that the speed of light is constant for all observers.

When Maxwell derived that the speed of light in the ether was 299,792,458 m/s could he or did he surmise that the speed of light is constant for all observers (regardless of the motion of the source)?
No, it took Einstein to make that leap.

Staff Emeritus
No, it took Einstein to make that leap.
I'm not sure that's exactly true. It was well known by Einstein's time that Maxwell's equations predicted that speed of light is constant independent of the motion of the source. This was generally thought of as a flaw in the theory and that Maxwell's equations were approximate and would need to be modified. Einstein's contribution was to take this feature seriously.

Khashishi
Maxwell thought electromagnetism was carried in some kind of luminiferous aether. I suppose it was understood that the speed of light would be relative to the aether. Lorentz eventually came up with a theory in which the speed of light was invariant, but still held on to the concept of aether.

We are done with aether now, it does not fit with observation.
Dark matter is what though?, not aether but it is there (apparently)

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tech99
Gold Member
Maxwell thought electromagnetism was carried in some kind of luminiferous aether. I suppose it was understood that the speed of light would be relative to the aether. Lorentz eventually came up with a theory in which the speed of light was invariant, but still held on to the concept of aether.
May be wrong but not certain that Maxwell did suppose the existence of an aether. He produced equations which fit the facts by postulating a mechanical analogue using rotating cells. He did not seem to propose an actual mechanism for EM phenomena.

Delta2
Homework Helper
Gold Member
May be wrong but not certain that Maxwell did suppose the existence of an aether. He produced equations which fit the facts by postulating a mechanical analogue using rotating cells. He did not seem to propose an actual mechanism for EM phenomena.
Maxwell worked a lot in the aether theory. In his 1873 paper "Treatise on Electricity and Magnetism" aether is mentioned as the medium in which EM waves and light propagate. But even at that time the properties of aether were considered sort of magical.

from Wikipedia: https://en.wikipedia.org/wiki/Luminiferous_aether

Wikipedia said:
the aether was hypothesized as the absolute and unique frame of reference in which Maxwell's equations hold. That is, the aether must be "still" universally, otherwise c would vary along with any variations that might occur in its supportive medium. Maxwell himself proposed several mechanical models of aether based on wheels and gears..

phinds
Gold Member
I'm not sure that's exactly true. It was well known by Einstein's time that Maxwell's equations predicted that speed of light is constant independent of the motion of the source. This was generally thought of as a flaw in the theory and that Maxwell's equations were approximate and would need to be modified. Einstein's contribution was to take this feature seriously.
Right. That's the "leap" that I was talking about. Maybe it's just me but I've always thought that THAT leap was the hard one and the one he didn't make (that the universe wasn't static) would have been an easier one. I mean, to me the speed of light thing is just weird and it astounds me that anyone could make that leap. 'Course I couldn't have made either one of them I'm sure.

We are done with aether now, it does not fit with observation.
Dark matter is what though?, not aether but it is there (apparently)
None of these fit the observation [yet] (even the LUX experiment for detecting dark matter is failing, even after reaching its maximum resolution). There are also Einstein-aether theories for dark energy, but they are also failing.
Aether was abandoned after the Michelson-Morley experiment ...

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